How Do Douglas Low Voltage
Lighting Controls Work?

Basics

All lighting controls utilize some sort of electrically controlled device that turns the load ON, OFF or in some cases dims the load. The device is in turn controlled by a wall switch, sensor, time clock and/or automation device. This strategy permits a variety of options that can make load control easier (or even possible in some cases) and can save considerable energy with the application of automation.

The Douglas 2-Wire Relay

The foundation of the Douglas lighting control system is the Douglas 2-wire latching relay. Douglas 2-wire latching relays have several inherent features that are highly suitable for lighting controls.

Douglas Relays are Designed for Lighting Loads

Lighting loads are very harsh loads to switch. Relays or contactors that are not rated for lighting loads will wear out prematurely. Douglas relays are engineered for all types of lighting loads to give decades of reliable service.

Douglas Relays are Easy to Wire

The Douglas 2-wire relay can be switched and can indicate status with one control wire. When connecting switches, there is only one control wire from the switch to the relay, not 2 or 3. Thus, wire management is greatly simplified.

Douglas Relays are Powered ON and Powered OFF

There are a number of benefits from this feature:

1. Once the relay is ON or OFF, it remains in that state and requires no control power to stay ON or OFF. Thus, relays hold their state even when the relay panel’s control power is lost.

2. Many relays can use the same control power source (a transformer). Wiring is simplified, as relays, switches and control devices can share the same common wire for power.

3. The same relay can be easily controlled by multiple devices. This makes it easy to apply different lighting controls to the same relay:
   • Wall switches (installed on the wall)
   • Sensors (installed at sensing location)
   • Automation devices (installed in the panel)
   • Time controlled devices (installed in the panel)
   • Control by Building Management Systems

A common lighting control combination example is an individual room switch to allow occupant control and an automation device installed in the panel and connected to the same relay to provide automatic control.

Douglas Relays ON/OFF Status

Latching relays have a built-in indicator, a status feedback circuit and/or an auxiliary contact to report the ON/OFF status. You can tell if a Douglas relay is ON or OFF by:

1. The position of the built-in mechanical indicator. the mechanical indicator can also be used to manually switch the relay;

2. The switch LEDs, lit by the status feedback circuit;

3. Monitoring the status feedback circuit;

4. An auxiliary contact (optional for Douglas relays).

Knowing the relay status has many uses. At the panel, the status is shown by the relay. A remote lighting load’s status can be displayed on a switch. Automated lighting controls can detect status to perform timed ON functions, to log the relay ON time, to display the status on other devices such as a PC, or to broadcast the status to other systems.